I. Field of the Invention
This invention relates to a light-triggered semiconductor device, and more particularly to an improvement on the light-transmitting mechanism of said light-triggered semiconductor device which is intended to improve the light-transmitting efficiency and reliability of the device.
II. Description of the Prior Art
In recent years, a light-triggered semiconductor device has been widely accepted in which light triggering is effected by applying a light signal as a control medium. A conventional light-triggered thyristor is constructed as shown in FIG. 1. Reference numeral 1 denotes a light-triggered semiconductor chip (hereinafter referred to as "a chip"). The conventional thyristor is triggered by leading out a cathode and anode by a cathode electrode 2c and anode electrode 2a respectively pressed against a cathode electrode layer 1c and anode electrode layer 1a, and supplying a signal light to a light-sensitive area 1g positioned substantially at the center of the main plane on the cathode side. A light guide 3 allowing for the passage of the signal light is formed of an optical fiber. Part of that side of the light guide 3 which lies near one end face 3a thereof is fixed to the chip by an adhesive 4 in such a manner that said one end face 3a faces the light-sensitive area 1g. The light guide 3 is extended along an electrode 2c parallel with the main surface of the chip 1 through a pipe 6 penetrating the peripheral wall 5 of an envelope. The other end face 3b of said light guide 3 faces a light-receiving window 7.
In the conventional technique there is great difficulty in exactly fitting one end face 3a of the light guide 3 to a narrow light-sensitive area 1g. When the light guide 3 assumes the desired position indicated by solid lines in FIG. 2, a light-receiving region occupies an area (a). When, however, one end face of the light guide 3 is partly displaced as indicated by broken lines in FIG. 2, then the end face is partly set over the cathode electrode layer 1c mounted on the light-triggered semiconductor chip 1. At this time, a light-sensitive area occupies a smaller area (a') than the aforementioned proper light-sensitive area (a), thereby reducing the light-transmitting rate.
The above-mentioned conventional light-triggered semiconductor device in which one end face 3a of the light guide 3 is fixed to the chip by the adhesive 4 has the drawback that thermal or mechanical stress resulting from the operation of the thyristor tends to crack or break the light guide 3. This event arises from the difference between the thermal expansion coefficient of copper constituting the main electrode and that of glass. The thermal stress calculated with respect to a light guide 50 mm long runs as follows:
Thermal expansion coefficient of copper . . . 17.times.10.sup.-6 (deg.sup.-1) PA1 Thermal expansion coefficient of glass . . . 0.5.times.10.sup.-6 (deg.sup.-1) ##EQU1## then, .DELTA.dl=(17.times.10.sup.-6 -0.5.times.10.sup.-6).times.50.times.100=0.0825 mm
This Calculation Shows that the above-mentioned thermal stress is quite large.